华工计算机大三上学习软件工程ch

1、Software EngineeringRequirements engineering processesIntroductionvGoal of requirements engineering processAssessing whether the system is useful to the business (Feasibility study)Discovering requirements (elicitation and analysis)Converting these requirements into some standard form (specification

2、)Checking that the requirements actually define the system that the customer wants (validation)The requirements engineering processelicitationspecificationvalidationFeasibility studiesvFeasibility studyFeasibility study answersvDoes the system contribute to the overall objectives of the organization

3、vCan the system be implement using current technology and within given cost and schedule constraintsvCan the system be integrated with other existed systems Requirements elicitation and analysisvRequirements elicitation and analysisvSoftware engineers work with customers and system end-users to find

4、 out about the application domain, what services the system should provide, the required performance of the system, hardware constraints, and so on.StakeholdersvRefer to any person or group who will be affected by the system, directly or indirectly.Requirements elicitation and analysisvDifficult to

5、elicit and understand stakeholder requirementsStakeholders often dont know what they want from the computer system Stakeholders naturally express requirements in their own terms and with implicit knowledge of their own workDifferent stakeholders have different requirements, which they may express in

6、 different waysvRequirements discoveryvRequirements classification and organizationvRequirements prioritization and negotiationvRequirements documentationRequirements discoveryvRequirements discoveryvSources of information: documentation, system stakeholders and specifications of similar systemsTech

7、niques of requirements discoveryvInterviewing, scenarios and ethnographyvStructured analysis methods, system prototype, Object-oriented analysis.Requirements discoveryViewpoint-oriented approachv a key strength of viewpoint-oriented analysis is that it recognizes multiple perspectives and provides a

8、 framework for discovering conflicts in the requirements proposed by different stakeholders LIBSYS viewpoint hierarchyvThe Volere requirements process model suggests some additional sources for requirementsViewpoint-oriented analysisvViewpoint identification and structuring;vViewpoint documentation;

9、vViewpoint requirements analysis and specification.IdentifyviewpointsDocumentviewpointsAnalyserequirementsAbstract viewpoints andabstract requirementsSpecifyrequirementsValidaterequirementsIdentifiedViewpointsDocumentedviewpointsViewpointinformationstructureNegotiatedrequirementsRequirementsspecific

10、ationRequirements spaceATM viewpointsBank customerHome customerSecurity officerBankBank staffBank managerBank tellerATM operatorCustomer databaseCard database2Operator2.1Foreign customerBank customer2.2Bank customer1OperatorBank staff1.1Bank staff1.2Bank staff1.33Organisation4OrganisationSystem5Syst

11、em6ViewpointRequirementIdentifier.LabelDescriptionTypeSourceVP1Bank staff1.1 Provide access to administrative services based onvalid staff PIN and the access permissions set outfor the bank staffsv41.1Bankmanager1.1.1 Provide transaction reports to bank manager.1.1.2 The bank manager requires transa

12、ction reports tobe provided on a daily basissvsv1.11.11.2Bank teller1.2.1 Provide for cancellation of cash card in the eventof lose or cancellation of card by bank.1.2.2 Provide for card cancellation effected in no morethan 3 minutes from request.svnf441.3ATMoperator1.3.1 Allow for system startup an

13、d shutdown based onvalid staff PIN from ATM operator1.3.2 Provide a facility for paging operator when fundsare low in ATM1.3.3 Failure rate of the paging service should notexceed 1 in 1000 attemptssvsvnf443ViewpointRequirementIdentifierLabelDescriptionTypeSourceVP2Bank customer2.1 Provide access to

14、ATM services based onvalid cash-card, valid PIN and accesspermissions set out for the bank customer2.2 Provide for withdrawal of cash by bankcustomers2.3 Cash withdrawal service should beavailable 999/1000 requests2.4 Cash withdrawal service should have aresponse time of no more than 1 minute2.5 At

15、least 50% of the currency notes in theATM should be 5 and 10 dollars notes.svsvnfnfnf442222.1Home customer2.1.1 Provide home customers with the facilityto transfer funds2.1.2 Provide home customers with the facilityto obtain a printout of their last fivetransactions2.1.3 Provide for balance enquiry

16、by bankcustomerssvsvsv4442.2Foreign customerViewpointRequirementIdentifierLabelDescriptionTypeSourceVP3Security officer3.1 All system security risks shall be identified,analysed and minimised according to theALARP (as low as is reasonably possible)principle.3.2 Standard encryption algorithms shall b

17、e used.3.3 System shall print paper record of alltransactionsnfnfnf4444Bank4.1 Complete system maintenance shall be doneonce every month.4.2 Cash withdrawal service should be availablein 90% requests for the service.4.3 Cash withdrawal should have a response timeof no more than 2 minutes from the ti

18、me ofrequest4.4System shall be operational in 6months4.5 System should accommodate all currentcurrency notesnfnfnfnfnf444445Customerdatabase6Card databaseConstraints on servicesViewpoint ServiceIdentifierdescriptionConstraintAll services4.1 Complete system maintenance to be done once every month4.4

19、System must be operational in 6 months1.1.1Transaction reports1.1.2Transaction reports must be provided on a daily basis1.2.1Card cancellation1.2.2Service should have a response time of no more than 3minutes1.3.2Operator paging whenfunds are low in ATM1.3.3Failure rate of the paging service should n

20、ot exceed 1 in10000 attempts2.2Cash withdrawal2.3Cash withdrawal service should be available 999/1000requests2.4 Cash withdrawal service should have a response time of nomore than 1 minute2.5 At least 50% of the currency notes in the ATM should be 5and 10 dollars bills.4.2 Cash withdrawal service sh

21、ould be available 9/10 requestsfor the service4.3 Cash withdrawal should have a response time of no morethan 2 minutes19Conflict analysisvConflicts may arise from contradictions among individual viewpoint requirements.Examples include:vwhere the service provision across viewpoints is associated with

22、 different constraints of the same general typevwhere the provision of a service across viewpoints is associated with similar constraints; but differing constraint valuesConflict analysis (example) ID2.34.1 Description Requirement 2Cash withdrawalservice should beavailable in 999/1000requestsComplet

23、e systemmaintenance must bedone once everymonthIDDescription2.3Cash withdrawal service should be available999/1000 requests-2.4Cash withdrawal service should have a responsetime of no more than 1 minute2.1.3Provide for balance enquiry by bank customers?3.1All system security risks must explicitly id

24、entified,analysed and minimised according to the ALARP(as low as is reasonably possible) principle.c4.1Complete system maintenance must be done onceevery month-4.3Cash withdrawal should have a response time ofno more than 2 minutes from the time of request4.4System shall be operational in 6 monthscR

25、equirement 1Requirements discoveryvInterviewingvPuts questions to stakeholders about the system, Requirements are derivedvClosed interviews, a predefined set of questionsvOpen interviews, there is no predefined agendaRequirements discoveryvScenariosvThey can understand and critique a scenario of how

26、 they might interact with a software systemA scenario for article download in LIBSYSArticle printing use-caseLIBSYS use casesArticle printing详细用况说明的结构用例的组成部分用例的组成部分注注 释释用例名称用例名称以动词开始以动词开始范围范围要设计的系统要设计的系统级别级别“用户目标用户目标”(基本流程基本流程)或或“子功能子功能”主要参与者主要参与者调用系统以提供服务的参与者调用系统以提供服务的参与者涉众及其关注点涉众及其关注点关注该用例的人，以及他们各

27、自的需要关注该用例的人，以及他们各自的需要前置条件前置条件用例启动前必须成立的条件用例启动前必须成立的条件后置条件后置条件用例结束后必须成立的条件用例结束后必须成立的条件主成功场景主成功场景典型的、理想的成功场景典型的、理想的成功场景替换场景替换场景其它可能的场景（成功或失败）其它可能的场景（成功或失败）特殊需求特殊需求相关的非功能需求相关的非功能需求技术和数据变元表技术和数据变元表不同的不同的I/O方法及数据格式方法及数据格式发生频率发生频率当前用例的发生频率，可能影响调查、测当前用例的发生频率，可能影响调查、测试和实现的时间安排试和实现的时间安排其它问题其它问题仍待解决或确认的问题仍待解决

28、或确认的问题POS系统收银用况详细说明-1范围：范围：下一代下一代POSPOS系统系统级别：级别：用户目标用户目标主要参与者：主要参与者：收银员收银员涉众及其关注点：涉众及其关注点：收银员：准确、快速地完成收银操作收银员：准确、快速地完成收银操作顾客：快速完成付款并获得购物凭证以方便退货顾客：快速完成付款并获得购物凭证以方便退货前置条件：前置条件：收银员经过认证、顾客是超市会员收银员经过认证、顾客是超市会员后置条件：后置条件：正确更新库存、正确计算税金正确更新库存、正确计算税金POS系统收银用况详细说明-2主成功场景：主成功场景：1.1.顾客携带商品到收银台付款顾客携带商品到收银台付款2.2.

29、收银员启动一次销售过程收银员启动一次销售过程n.n.顾客付款系统打印票据完成整个销售过程顾客付款系统打印票据完成整个销售过程替换场景：替换场景：a.a.顾客信用卡额度不足要求退货顾客信用卡额度不足要求退货b.b.条码无法刷出使用键盘输入唯一码条码无法刷出使用键盘输入唯一码特殊需求：特殊需求：1.90%1.90%情况下信用卡刷卡响应时间小于情况下信用卡刷卡响应时间小于3030秒秒2.2.顾客能在顾客能在1 1米范围内清楚看到单价和累计金额显示米范围内清楚看到单价和累计金额显示POS系统收银用况详细说明-3技术与数据变元：技术与数据变元：1.1.商品商品IDID获取可以通过扫描和键盘输入两种方式获

30、取可以通过扫描和键盘输入两种方式2.2.商品商品IDID支持中国、欧洲及日本三中编码标准支持中国、欧洲及日本三中编码标准发生频率：发生频率：可能在可能在1616小时内不间断发生小时内不间断发生其它问题：其它问题：1.1.收银员下班后是否需要清理现金并进行结帐处理收银员下班后是否需要清理现金并进行结帐处理2.2.该超市是否可能在未来实行该超市是否可能在未来实行2424小时营业小时营业EthnographyvEthnographyvAn analyst immerse him or herself in the working environmentvIt helps analysts disco

31、ver implicit system requirements that reflect the actual Ethnography and prototypingv快速原型模型快速原型模型需求调研例学生选课系统-1v第一阶段：了解基本情况请教务处老师介绍背景，如学生总数、课程数量、选课相关的基本制度等v第二阶段：制订访谈计划，深入讨论相关需求除了学生还有哪些相关用户?选课规则(学分、课程人数限制等)、退课规则了解客户对系统的期望：准确、访问速度快需求调研例学生选课系统-2v第三阶段：基本了解需求后就一些关键细节通过问卷进行明确在已经了解总体选课人数之后，需要进一步了解通常情况下的选课持续

32、时间、是否按院系逐步开放选科、选课人数的一般分布等与性能设计密切相关推荐关键管理人员使用USB Key设备，经济上是否可以接受v原型：如该企业有类似成熟系统可结合系统演示进行需求调研需求建模 v在软件需求分析阶段，所创建的模型，要着重于描述系统要做什么，而不是如何去做v目标软件的模型不应涉及软件实现细节v常用的分析方法：面向数据流的结构化分析方法 (SA)面向数据结构的分析方法 面向对象的分析方法 (OOA)Requirements validationvRequirements validationvIs concerned with showing that the requirements actually define the system that the customer wantsChecks includevVal